Alarm system



Jan. 12, 1960 B, Z|MMERMAN 2,921,299

ALARM SYSTEM Filed'Feb. 10, 1958 FIG 2.

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ALARM SYSTEM Benjamin E. Zimmerman, Conger-ville, Ill.

Application February 10, 1958, Serial No. 714,247

2 Claims. (Cl. 340-274) This invention relates to protective devices forlocks. While it has particular application to alarm systems forautomobile ignition switch locks, its application is not limitedthereto.

The enormous number of car thefts in the United States each year, is amatter of common knowledge. It is desirable both to make such theftsdifficult, and to apprehend those who are predisposed to stealautomobiles. The problem is not a new one. A patent to Stone, No.1,351,973, issued September 7, 1920, discloses a device in circuitwiththe ignition switch of a motorvehicle, whereby an alarm is soundedif the ignition switch is tampered with. The Stone device, and that ofLodispoto, No. 2,011,944, issued August 20, 1935, depends upon, themovement of tumblers within the ignition lock, the insertion of a falsekey leading 'to the setting off of an alarm. However, the use of falsekeys has lost its vogue among modern car thieves, who use jumpers,unless the owner leaves the key in the ignition.

One of the objects of this invention is to provide a simple, eifectivedevice for discouraging tampering with locks.

Another object is to provide an alarm devicewhich is likely to beactuated by one attempting to operate the lock without authority.

Still another object of this invention is to provide an alarm devicewhich will continue to operatefor a predetermined length of time afterit is started, even though the lock be returned to its originalposition, and which will reset itself automatically.

Other objects will become apparent to those skilled in the art in thelight of the following description and accompanying drawing.

In accordance with this invention, generally stated, an alarm device isprovided for a key operated lock, which alarm device is operated by theuse of a false key Whichis deliberately inserted in the lock when thelock is to be left unattended. The presence of the key encourages thewould-be thief to use it, rather than using a jumper or otherwisebypassing or jimmying the lock. The false key is arranged to trip adevice which sounds an alarm for a predetermined length of time, Whetherthe false key is returned to its original position or not. At the end ofthat predetermined time, if the false key has been returned to itsoriginal position, the alarm will shut off and the device will resetitself automatically. If the key is not returned to its originalposition, the alarm will continue to sound.

In the drawing,

Figure 1 is a somewhat diagrammatic view in side elevation, partly insection, of a device constructed in accordance with one illustrativeembodiment of this invention;

Figure 2 is a sectional view taken along the line 2-2 of Figure 1; and

Figure 3 is a view in side elevation of an operating key.

v United States Patent F Patented Jan. 12, 1960 Referring now to thedrawing for one illustrative embodi.nent of this invention, referencenumeral 1 indicates a tumbler-type lock, adapted to be operated by a key2. A false key 3 is designed to fit into the lock 1, but is providedwith an extension or tab 6 which, when the key 3 is'in place in thelock, projects beyond the tumblers and into a slot 8 in a disc 10 of analarm device. In this embodiment, the dotted disc is the operatingmechanism.

The disc 10 is mounted for rotation. In the diagrammatic view shown inFigure l, the disc 10 is mounted on a post 12 secured to a base 14, Thedisc 10 has a cam 16 projecting from itsperiphery. The cam 16 engagesthe underside of a contact bar 20, which is pivoted on a pivot pin 22.The pivot pin 22 extends diametrically through a hollow post 24. The bar20 extends through the hollow post 24 diametrically, at right angles tothe pin 22. To this end, slots 26 are provided in the hollow post 24,through which the bar 20 extends. Within the hollow post 24, below thebar 20, is a coil spring'30, compressed between the underside of the bar20 and the top of the base 14. An upper spring 32 is compressed betweenthe top side of the bar 20 and a threaded plug 34 in the hollow post 24.The springs 30 and 32 are loosely enough confined 'within the hollowpost 24 to serve as overcentering devices. In the position of the bar 20shown in solid lines in Figure 1, upper spring 32 is shifted to theright of the pivot 22 and lower spring 30 is shifted to the left of thepivot, as viewed in that figure, in which positions they bias the bar 20to a position with its right end depressed and its left end elevatedfrom the horizontal. When the right end of the bar 20 is elevatedagainst the bias of the springs 30 and 32 until the right end of the bar29 is above the horizontal and left end of the bar 20 is below thehorizontal, the positions of the springs 30 and 32 are reversed, withthe upper spring 32 displaced to the left of the pivot and the lowerspring 30 displaced to the right of the pivot, as viewed in Figure 1.Under these circumstances, the bar 20 will be maintained in the postionshown in dotted lines in Figure 1, untilit is moved against the bias ofthe springs 30 and 32 to restore it tothe position shown in solid linesin Figure 1.

Mounted on the base 14 on the opposite end of the base from the disc 10,with respect to the post 24, are a contact bracket 40 and a resettingdevice 50.

The contact bracket 40 has an adjustable contact 41.

The resetting device 50,-shown somewhat diagrammatically in Figure 1,has a bimetallic strip 51 mounted on a spool 52 of refractory material.A heating element 53 isshown as wound on therefractory spool 52,,andconnected electrically to the bimetallic strip 51. The bimetallic strip51 carries an adjustable contact 54. The bimetallic strip 51 is normallyelliptical, as shown in solid lines in Figure 1, but has the property ofbecoming circular when heated and free to move, as indicated by dottedlines in Figure 1.

In this embodiment, the bar 20, contact bracket 41) and resetting device50 are all parts of an electrical circuit 60, which also includes apower source 65 and an alarm device 70. The power source 65 may be anysuitable and convenient power source. In an automobile, it will be thebattery. The alarm device 70 may take the form of lights, horn, bells,or any other suitable visual terial. However, asispointedouthereafter,thisarran ment is merely illustrative.

The heating element 53, hence the bimetallic element is c nnec ed byrcon uctor 67 10.-the n ga ive si of h PQ nsQum hS. 'Ih alarm d v eefl liislalso connected, i ser s wi t e cont t b a k t :tout conductor 6'],hence to the negative side of gtherpower source.

In operation, if the ope ating ikey 2 -is inserted in the lock, itextends, as indicated in dotted lines in Figure 2, far enough to operatethe lock, but not far enough to reach the disc 10. Accordingly, thealarm apparatus remains unaffected by theturning of the key.

When the false key 3 is in position, however, ;the'tab 6, extendingthrough ,theslot 8, operates to rotate the disc 10 when thekey 3,'isturned. Stops, not here shown, serve to prevent the jalse keys beingturned ,far enough to operate the lock. Therotation of the disc,10causes the cam 16 to move the bar 20 to the position shown in dottedlines in Figure 1. This causes the springs 30 and 32 to move overcenter, to maintain the bar .20 in the position shown in dotted lines,even though the key 3, hence the disc 10, is restored to its originalposition. With the bar 20 in the position shown in dotted lines, itmakes contact with the adjustable contact 4110f the contact bracket 40,and with the adjustable,contact,,54 of the bimetallic strip 51. Thiscompletes a circuit from the positive side of the power source 65,hrough the bar 20, contact 41, contact bracket 40, alarm device 70, andconductor 67 to the negative side of the power source; and through thebar 20, contact 54, bimetallic strip 51, heating element 53 andconductor '67 to the negative side of the power source 65. The efiect ofthe completion ofthese circuits is to cause the alarm deviceto operate,and at the same time to start the heating of the heating element 53,which heats the bimetallic strip .51, tending to cause it to assume thecircular configuration shown in dotted lines in Figure 1. If the key 3has not been turned back to its original position, the cam 16willmaintain the bar 20, against the bias of the bimetallic strip 51, incontact with the contact 41, allowing. the alarm device to continue tooperate. If the key 3,has been returned to its original position, theheating of the bimetallic strip 51 will cause the bar 20 to, be raisedabove the horizontal, at whichtime the springs 30 and 32 will reversetheir positions and restorethe bar 20 to its initial position. In itsinitial position, the bar ,20is out of contact with the contact 54 ofthe bimetallic strip 51, even in the circular position of thatbimetallic strip, so that when the springs30 and 32 move over center,they break the contact between the bar 20 and the heating element 53,permitting the bimetallic strip to cool and to return to its originalelliptical condition. It can be seen that by regulating the strength ofthe springs 30 and 32, and by providing suitable heating elements 53,the length of time during which the alarmdevice will .beoperated, whenthe key ,3. is immediately restored .to-its original position, can bemade of any desired duration.

Numerous variations in the construction of the alarm device of thisinvention, within the scope of the appended claims, will become apparentto those skilled in the art in the light of the foregoing disclosure.For example, it is not at all necessary for the bar 20 to be made ofelectrically conducting material. The bar may be made of anon-conductor, carrying contacts connected with the conductor 66. Otherover-centering devices may be employed, and otherrestoring or resettingmeans, such, for example, as a timer-actuated resilient biasing means,.althoughthe means specifically described have advantages in simplicityand cheapness. To earns 16 may be provided on the disc'-10,so thatthe-key'qnay be turned in either direction to raise the bar 20, and amember of difierent shape may be substituted for the disc.

A spring may be attached to the disc 10, to restore it immediately toits neutral position when the key 3 is released. A switch may beprovided in the circuit 60, or a device for restoring the bar 20 to itsoff position may be provided, to permit the alarm to be turned off,

1 if desired.

Thus it can beseen that a simple, dependable device isprovided fordiscouraging tampering with .locks, and for facilitating theapprehension of tamperers.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

1. An alarm device for a lock operated by a key, comprising a falsekeyadapted to fit the lock, said key having altab projecting beyond saidlock, an operating mechanism engaged by said tab, a contact bar arrangedto be rocked by said operating mechanism to operativeposition,,over-centering means adapted to bias said contact-barin eitheroperative or inoperative position, resetting means actuated, uponmovement of said contact bar, to operative position, to bias saidcontact bar to inoperative position counter to the bias of theovercentering means, an, electric power source electrically connected onone side with said contact bar, an alarm device connected with the otherside of said power source, and contact means connected with said alarmdevice and positioned to make electrical contact with said contact barwhen said contact bar is in operative position.

2. The device of claim 1 wherein the resetting means comprises abimetallic strip adapted to move when heated to contact-bar biasingposition, and a heating element connected with one side ofthe powersource and adapted to be connected to the other side of said source whenthe contact bar is moved to its operative position.

References Cited in the file of this patent UNITED STATES PATENTS

